Aluminised PET Film

This delicate, sleek material is an elegant compromise between a plastic sheet and an aluminium foil. It flops, flexes and weighs just like a thin plastic sheet, but it blocks light, heat, moisture and oxygen and conducts electricity just like a piece of aluminium foil. It is a film of polyethylene terephthalate or PET (a lightweight plastic of the polyester family, used for drink bottles and for clothing fibres), about as thick as a human hair. It has an ultra-thin aluminium coating of only a few hundred to a few thousand atoms thick. Those atoms are deposited onto the plastic via a method called physical vapour deposition: the metal is heated, evaporates under vacuum, and the metal vapour atoms condense onto the cold plastic sheet, forming a layer much thinner than the thinnest aluminium foil.

It is a cousin of aluminised Mylar, the trade name of a specific type of aluminised PET film, in which the plastic film is drawn in two perpendicular directions during its manufacturing, to align the long plastic molecules. This gives more mechanical resilience and a better optical clarity than non-oriented PET films like ours. 

Metallised PET films are found everywhere, from bags of ground coffee and space blankets to party balloons and antistatic pouches for electronic components. They are widely used in the food packaging industry because of their excellent barrier properties against gases, in particular water vapour and oxygen: they can keep chocolate chip cookies soft and moist, and crisps dry and crunchy. This specific material, though, was likely optimised for its optical properties. With the mirror-like finish of the metallised film, the sheet feels very much like a flawless, flexible, and featherweight mirror, and was probably developed with applications in mind which leverage these qualities. On the other side of the metallic coating, the plastic is backed with an adhesion-promoting layer, which help inks or graphics bind to the material.